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anonymous

  • 5 years ago

If y changes at a rate exactly three times its values and y(1)=4e, find y(5). This confuses me to the T.

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  1. anonymous
    • 5 years ago
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    it is given that dy = 3y. You can take it from there.

  2. anonymous
    • 5 years ago
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    After you get that, do you integrate both sides?

  3. anonymous
    • 5 years ago
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    the problem is not clear. does y change at a rate exactly three times its previous value?

  4. anonymous
    • 5 years ago
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    I would assume so because it does say values...does that help any?

  5. anonymous
    • 5 years ago
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    well, if y(1) = 4e, then y(2) = 3 times 4e and y(3) = 3 times 3times 4e and so on

  6. anonymous
    • 5 years ago
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    hmm so that would be 105e? That doesn't feel right, but I mean the steps make sense.

  7. anonymous
    • 5 years ago
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    otherwise it would be dy = 3y ==> y = 3y2 +c 3y^2 -y +c = 0. substitute y(1) = 4e and solve for c then use that to find y(5)

  8. anonymous
    • 5 years ago
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    no wait. that is wrong. scrap that.

  9. anonymous
    • 5 years ago
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    The second one or both?

  10. anonymous
    • 5 years ago
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    the second one.

  11. anonymous
    • 5 years ago
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    So, the first one was indeed right?

  12. anonymous
    • 5 years ago
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    I think so. Is this problem in application of derivatives or integrals or something?

  13. anonymous
    • 5 years ago
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    they have given y(1) = 4e. what is the 1? is it y at 1 second? is y a function of time?

  14. anonymous
    • 5 years ago
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    I'm not really sure...I'm just doing a huge packet of practice problems to help me study for the AP calculus test.

  15. anonymous
    • 5 years ago
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    I can't see it being a function of time...There is not information relating the problem to time.

  16. anonymous
    • 5 years ago
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    where rate is given, it is generally a function of time.

  17. anonymous
    • 5 years ago
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    Oh, I completely overlooked the rate of it all.

  18. anonymous
    • 5 years ago
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    so dy(t)/dt = 3y(t-1) ?

  19. anonymous
    • 5 years ago
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    Yes, so is that just the original function of y or is this y at 1?

  20. anonymous
    • 5 years ago
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    no, it is the general function of y.

  21. anonymous
    • 5 years ago
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    Okay, but why is the variable "y" in the function? It don't think that y should be in there. It's like putting a f in the function.

  22. anonymous
    • 5 years ago
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    because it is given that it changes at 3 times its values.

  23. anonymous
    • 5 years ago
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    Ahhhh haaa!

  24. anonymous
    • 5 years ago
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    yes, a function can depend on its previous values. you can put an f in the function.

  25. anonymous
    • 5 years ago
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    hmmm...well how would be begin to figure out y(5)'s function given that y(1)=4e? There is no "t" in "4e"..

  26. anonymous
    • 5 years ago
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    no no, t = 1.

  27. anonymous
    • 5 years ago
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    I think my first method was correct. there is no other explanation with the data given. so yeah. I guess 105e is your answer.

  28. anonymous
    • 5 years ago
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    just post your question and your answer, 105 e in a new post and see what everyone else thinks of the answer.

  29. anonymous
    • 5 years ago
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    Okay, that sounds better. I felt like through the second route, we were reading too much into the question...hmmm maybe...idk...I will try it. I do appreciate all of your help though, Thank you so much.

  30. anonymous
    • 5 years ago
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    you are welcome.

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